In recent years, there have been widely studied a method of producing a sugar solution by hydrolysis of a cellulose-containing biomass using cellulase, of which energy consumption and environmental burdens are low. However, the greatest defect of the method of producing a sugar solution using cellulase is the point that the production cost of a sugar solution increases due to the high price of cellulase. Although there has been proposed a method of recovering and reusing cellulase used for hydrolysis to solve such a technical problem, it is a problem that reusability is low since cellulase strongly adsorbs the hydrolysis residue produced upon hydrolysis of the cellulose-containing biomass.
As a method of reducing adsorption of cellulase to the hydrolysis residue, a method of adjusting the electrical conductivity of the reaction liquid to 5 to 25 mS/cm by adding a water-soluble salt upon hydrolysis of a cellulose-containing biomass (JP 4947223 B1), a method of adding calcium carbonate particles at an amount of 1 to 10% by weight based on the weight of a solid of a cellulose-containing biomass (JP 2012-100617 A), and the like are known.
As described above, a wide variety of attempts to reduce the amount of use of cellulase by recovering and reusing cellulase used for hydrolysis of a cellulose-containing biomass are made. However, since cellulase strongly adsorbs the hydrolysis residue, the recovery rate is low, and the problem has not been solved yet. It could therefore be helpful to provide a method of producing a sugar solution, wherein cellulase can be recovered more efficiently than in a conventional method.